Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $149.39   9.311%   $163.2997   $163.30   $163.30   $163.30  
  Purchase #2 $192.59   9.797%   $211.458   $211.46   $211.45   $211.50  
  Purchase #3 $119.29   7.174%   $127.8479   $127.85   $127.85   $127.80  
  Purchase #4 $234.73   4.138%   $244.4431   $244.44   $244.45   $244.40  
  Purchase #5 $24.41   3.139%   $25.1762   $25.18   $25.20   $25.20  
  Purchase #6 $54.30   3.655%   $56.2847   $56.28   $56.30   $56.30  
  Purchase #7 $180.26   8.596%   $195.7551   $195.76   $195.75   $195.80  
  7 purchase totals = $954.97       $1,024.2647   $1,024.27   $1,024.30   $1,024.30